Hypoid gears are generally formed with a cutting machine that rotates both a cutter tool and a stock piece of metal while the axes of rotation of the cutter tool and the stock are orientated at an angle. The cutter tool and/or the stock are advanced toward one another, generally along the axes of rotation as the blades of the cutter tool shave material from the stock to form gear teeth on the stock. Some machines will vary the orientation of the cutter tool and/or stock perpendicular to the axis of rotation during cutting to form a desired hypoid tooth shape. Both pinion and ring gear of a hypoid gear set are cut in this manner. Typical cutting machines are disclosed in U.S. Pat. Nos. 5,116,173 to Goldricil, and 5,662,514 to Masseth, the disclosures of which are hereby incorporated by reference in their entireties.
Typically, a single cutter tool contains blades that are dimensioned to form a single gear for a single gear ratio (i.e. number of gear teeth/number of pinion teeth). That is, a cutter tool assembled with blades designed for cutting a ring gear with a gear ratio of 4.11 to 1 can not be used to cut a ring gear of a different gear ratio, and cannot be used to cut a pinion gear. In the example of a gear ratio of 4.11 to 1, a typical pinion for a vehicle differential has 9 teeth and the ring gear has 37 teeth. Many cutter tools may be dimensioned such that different blades may be used to form different gears of different gear ratios, but typically, the blades for forming the different gears are not common. That is, typically, a gear cutting tool includes a plurality of inside blades and a plurality of outside blades extending therefrom for forming the teeth of a hypoid gear. Typically, the inside blade forms the drive side of a hypoid ring gear tooth, and the outside blade forms the coast side of a hypoid ring gear tooth.
With continual development in blades, the life of a blade is extended due to, for example, tip coatings and blade materials and treatments. These developments permit blades to last longer and permit cutter tools to be used for longer periods of time between blade replacement.